This invention relates to footers used to support constructed structures.
The general concept of a footer is to spread an overlying load over a large enough area of underlying soil or rock that the load-bearing capacity of the soil or rock is not exceeded.
Specifically, the function of a footer is                (i) to receive a downwardly-directed, gravity-initiated force from an overlying load such as a wall, a roof, or the like,        (ii) to laterally and longitudinally distribute that load over an area greater than the cross-sectional area of the overlying load/wall at the upper/contact surface of the footer, and        (iii) to deliver that so-distributed load to the underlying soil or rock over that greater area, at the lower surface of the footer.        
By so distributing the load, and applying the load to the underlying soil over a greater area, the footer does two things. First, the footer distributes any point loads or concentrated loads by spreading such loads over a greater area; which means that the magnitude of the load in any micro area is attenuated. Second, the width of the footer is generally greater than the width of that wall which applies the load onto the footer. By applying the total load to the underlying soil over a greater overall area/width, the load per unit area, as applied to the soil, is generally lower than the load per unit area at the bottom of the wall which applied the load.
Thus, a footer allows the builder to construct a building, and keep that building stable, where the width of the upright wall of the building, as that wall approaches the underlying soil, applies a downward force which exceeds the load-bearing capacity of the soil given the cross-section of the wall which would apply that load to the soil. The footer thus serves as a transition element, and a transfer element, spreading the load over a great enough area of the soil that the soil can bear the load being transferred, without the soil being moved as a result of the load being applied.
Before constructing a building, such as a house, a cottage, a garage, an addition to an existing building, or any of a variety of commercial or industrial type buildings, the contractor first excavates a trench below the surface of the soil. If the structure is to include a basement, the trench will be excavated below and around the outer perimeter of the bottom of what will be the basement floor. The trench dimensions are specified according to the needs of the construction site and the construction project. In cold climates, the trench is usually dug to a depth which extends at least to a depth below the frost line, assuming no basement is first dug. In northern states, such as Michigan, Wisconsin, Minnesota, etc. the frost line is at a depth of about 42 inches. Thus, the bottom of a typical footer in that region, for a residential dwelling, is about 48 inches below grade.
For residential construction, a conventional steel reinforced concrete footer, itself, is about 16 inches wide by 8 inches in height so that such footer can support an overlying conventional exterior concrete wall of the building, which overlying concrete wall is typically about 8 inches thick. Larger size footers are used to support greater overlying loads, e.g. for commercial and industrial buildings, where the overlying e.g. building structure includes thicker and heavier walls, and may include metal crossbeams, where the structure is several stories in height, or where the structure is intended to house and/or support e.g. heavy machinery.
The footer extends around the outer perimeter of the structure and has approximately the same geometrical configuration as the exterior walls which enclose the e.g. building. For example, for a rectangularly-shaped house, a plan view of the footer expresses the footer as having a rectangular shape. Once the trench is dug, the contractor constructs a pair of vertical, spaced apart forms, usually of wood, wherein the tops of the forms terminate at the required height of the footer. Concrete is then poured into the footer forms, up to the tops of the wood forms, and is allowed to harden and cure. After the concrete has hardened, the wood forms are manually removed. The external walls of the building structure can be built upward from the upper surface of the footer once the concrete has cured.
Some drawbacks with this present system of constructing footers are that they are expensive and time consuming to install. Usually, one or two workers are required to construct the wood forms which outline the shape and height of the footer. If the workers are trained carpenters, their wages can be relatively high. Depending on the size of the building, it may take several hours to construct the wood footer forms. A fluid ready-mix concrete truck delivers the fluid concrete for the footer to the work site and again manual labor is needed to move, spread and vibrate the concrete into the wood forms. After the footer is poured, one then has to wait for the concrete to harden/cure before the wood forms can be manually removed. This wait time before the forms can be removed is typically a couple of days. It takes still longer for the concrete footer to fully cure, sometimes up to about 30 days, before one can construct load bearing exterior walls on the so-fabricated footer.
Conventionally, most footers are formed from fluid ready-mix concrete poured into a wood form. A typical footer extends around the outer perimeter of the building to be built. The wood form is manually constructed by carpenters or other skilled labor at the bottom of the trench 16. The wood form includes a pair of spaced apart side walls separated by intermittent spacing members. The length of the footer is specified according to the dimensions of the finished building. The wood at the side walls of the footer form is constructed to a predetermined height, usually about 8 inches above the underlying soil. Vertical studs can be secured to the footer side walls to keep the side walls from moving laterally and intermittent spacing members can extend between the side walls to keep the side walls properly spaced from each other. The wood forms do not include a bottom member or a top member. Fluid ready-mix concrete is poured into the wood form, up to the top surface of the side walls and is leveled off using a straight edge such as a wood 2 by 4. The concrete is usually moved and spread manually with a shovel and then may be subjected to vibration using a special vibration tool to settle the concrete and remove any air bubbles that may have become entrapped in the concrete.
The manual labor needed to construct a wood form and to pour a concrete footer can be rather extensive. Thus, the forming of a concrete footer is both expensive and time consuming. Another drawback to a concrete footer is that one has to wait for the concrete to set and harden before the wood forms can be removed. In addition, concrete takes up to 30 days to fully cure before it can support its full designed load, such as an external wall of the building.
Thus, it would be desirable to provide a footer product which can be emplaced in the footer trench without having to wait for any material to cure or harden before a building load can be applied.
It would also be desirable to provide a footer product which provides a thermal shock barrier.
It would further be desirable to provide a footer product which can be brought to the construction site with others of the non-mineral construction products which will be used to build the above-grade portions of the building.
It would be still further desirable to provide a footer product which is more environmentally friendly than concrete.
These and other needs are provided, or at least partially provided, by footer products of the invention.